Automatic by-pass valving systems and methods

ABSTRACT

An automatic by-pass valving system for an electrical cable system wherein insulating fluid at a pressure above atmospheric pressure is supplied to an electrical power cable, such as a pipe-type or self-contained cable, having a fluid flow channel and having at least one hydraulic stop interrupting the flow of fluid between the channels of adjacent portions of the cable which are at different elevations. The valving system comprises a check valve, which allows fluid flow only in a first direction, from the lower elevation portion to the higher elevation portion, and a flow-limiting valve, which allows fluid flow only in a second direction, from the higher elevation portion to the lower elevation portion, at a reduced rate. Preferably, a relief valve is also provided to allow fluid flow in the second direction at a higher rate if the fluid pressure difference in the second direction is exceeded by a predetermined amount. The valving system limits the loss of the insulating fluid from the cable when the lower elevation portion is ruptured, protecting the environment, while permitting a limited flow from the point of rupture to protect the cable from contamination.

This application is a division, of application Ser. No. 08/592,030,filed Jan. 26, 1996 now Pat. No. 5,865,212.

The present invention relates to automatic by-pass valving systems andmethods for electrical cables containing fluids under pressure and, moreparticularly, automatic by-pass valving systems and methods for limitingthe release of dielectric fluid from a ruptured, fluid-filled electricalcable, e.g. a pipe-type cable or a self-contained cable.

BACKGROUND OF THE INVENTION

Electrical power cable systems often utilize dielectric insulating fluidas a means of preserving the integrity of electrical cable insulationconstructed from dielectric fluid-impregnated electrical insulationmaterials and in some cases, for cooling of the cable. In a pipe-typeelectrical power transmission cable system, dielectric insulating fluidsurrounds insulated conductors within a pipe. In a self-containedelectrical power transmission cable system, dielectric insulating fluidis introduced into the cable system via one or more fluid passagesconstructed within the cable, and the fluid pressure is retained withinthe cable by the action of outer-non-permeable sheathing which surroundsone or more insulated conductors. As is known in the art, the fluid ismaintained under pressure by one or more external sources of fluid underpressure, such as pumping stations or pressurized fluid reservoirs andcan be static or circulated within the pipe or duct. When such pipe-typeor self-contained cables are run from points of lower elevation topoints of higher elevation, a pumping station at the lower elevationpoint can be used to pressurize or circulate the insulating fluid.However, the pumping station can be at the higher elevation point, orthere can be several pumping stations located at one or more end pointsand/or at points intermediate to the lowest elevation and highestelevation points.

Most modern dielectric fluids are synthetic in nature, while many olderinstallations contain oil-based dielectric fluids. Regardless of thespecific type of dielectric fluid under consideration, nearly allenvironmental regulatory agencies concur in that the release ofsignificant quantities of dielectric fluid into the environment ishighly undesirable. In fact, various state and local environmentalregulatory bodies have acted to restrict or eliminate the constructionof new fluid-filled cable systems, particularly if these new systemshave been designed without provision being made for the restriction offluid loss from the cable system. Furthermore, many electrical utilitycompanies who are possessed of large existing fluid filled cablesystems, representing tremendous capital investment, have been recentlypresented with mandates requiring the modification of these existingcable systems to incorporate such fluid loss restrictive provisions,particularly in the case of cable systems crossing or lying near notablebodies of water. Breaks or ruptures in the pipe or cable sheath cancause the unrestricted release of thousands of gallons of fluid, whichcan cause substantial losses of plant and animal life. In addition tothe environmental impact, replacement of the released fluid isexpensive. In addition, once the fluid has escaped from the cable, wateror dirt can enter the cable or cable system pipeline through the break.Such contamination of the cable or cable system pipeline by theenvironment can require the replacement of significant lengths of cable.

Although various types of electrical power transmission cables existwhich do not require the presence of fluid dielectric material, thesetypes of cables do not have the decades long history of reliableoperation at high voltages and high ampacities as do fluid-filled cablesystems. Also, the replacement of the hundreds of miles of existingfluid-filled cable systems, (in the United States mostly pipe-type cablesystems), with solid dielectric insulation cables would involve suchextraordinary cost as to be unfeasible. This solution to theenvironmental regulatory concerns stated previously becomes even moreunattractive when it is considered that the lower current carryingcapacity of solid dielectric insulation type cables would require that agiven number of existing pipe-type cable circuits be replaced with agreater number of solid dielectric insulation type cable circuits, ifthe operating voltages are left unchanged.

Superconducting cables are being developed which are intended to serveas transmission cable systems. For retro-fit pipe installations and newinstallations (utilizing superconducting cables), the cables beingdeveloped will utilize dielectric fluid impregnated electricalinsulation of a similar nature to that which is currently used as theelectrical insulation for pipe-type cables. In fact, the construction ofthese cables, as presently envisioned will be such that existing copperconductor type and aluminum conductor type pipe-type cable systems canbe retro fitted with the superconducting cable, leaving the pipe systemmanholes and pressure support equipment essentially unchanged.Obviously, with the operation of these superconductive cable systemsremaining dependent on the use of fluid dielectric materials within thesystem pipeline, the same concerns regarding the restriction ofdielectric fluid leakage from the pipeline apply.

To address these problems, well-known stop joints are typically providedbetween cable portions or sections to hydraulically isolate such cableportions or sections. The stop joint is a device which mechanically andelectrically interconnects cable sections, but which prevents the flowof the fluid directly from the pipe of one pipe cable section to thepipe of the next pipe section, in the case of pipe cables, or from thefluid duct of one self-contained cable to the fluid duct of the nextself-contained cable. However, each stop joint has manually operableby-pass valves and piping which interconnect one side of the stop jointwith the other side of the stop joint so that when the by-pass valvesare open, the fluid can flow therethrough and between the pipes or ductsof the cable sections connected to the joint. Such by-pass valves areusually accessed through a manhole.

In the event of a break in a pipe or duct of such a system and eventhough the break and reduction in pressure may be sensed at the pumpingstation, causing the pumping station to cease the supply of fluid, fluidin the pipe or duct at elevations above the rupture site, includingfluid above the nearest stop joint, flows towards the rupture site dueto gravity. Fluid from above the stop joint is lost through the ruptureuntil the rupture is located and the nearest by-pass valve above therupture is manually closed by maintenance crews, who must enter theappropriate manhole. Thousands of gallons of fluid can be lost beforethe proper valve is closed, causing severe damage to the environment andmonetary loss. Once the valve is closed and the fluid flow ceases, thecable is exposed to contamination from the environment.

One alternative to the manual by-pass valve is to put sensors and amotorized valve in the manhole. This is not cost effective, however. Itis also undesirable to provide electrical power in the manhole.

U.S. Pat. Nos. 5,207,243 and 5,280,131, both issued to Sarro, describe atwo way fluid flow check valve controlled by a piston within the valvehousing. Internal and external pressures move the piston towards thedirection of lower fluid pressure, closing the valve. When the valve isclosed, the flow of fluid from the cable portion or portions atelevations higher than the valve is prevented. Until the valve closes,however, such fluid flows out of the break. After the valve closes,fluid in the cable between the break and the valve continues to flow outof the cable through the break until there is only a small amount offluid in the portion of the cable between the break and the valve. Thecable is then subject to the risk of contamination at the break.

SUMMARY OF THE INVENTION

The present invention provides an automatic by-pass valving system whichcan be applied to fluid conveying pipes or ducts to enable flow of fluidbeyond a conventional fluid flow-isolator, such as a stop joint, and tolimit the loss of fluid caused by a break in the pipe or duct to alimited rate. The limited rate of flow prevents contamination of thecable but poses minimal risk to the environment.

In accordance with the preferred embodiment of the invention, theautomatic valve system comprises means including a check valve which canbe connected to the pipe or ducts so as to provide a first path forfluid flow around a device, such as a stop joint which interrupts theflow of fluid from one pipe or duct to another pipe or duct, only in thedirection from a portion of cable at a lower elevation to a portion ofthe cable at higher a higher elevation. The valve system also includesmeans including a flow limiting valve which can be connected to the pipeor ducts so as to provide a second path for limited fluid flow aroundsaid device in the direction from the portion of the cable at higherelevation to the portion of the cable at lower elevation. The valvesystem also includes means including a relief valve which can beconnected to the pipe or ducts so as to provide a third path for fluidflow from the portion of the cable at higher elevation to the atmosphereor to the portion of the cable at lower elevation when the fluidpressure difference between the fluid in the portion of the cable athigher elevation exceeds the fluid pressure in the portion of the cableat lower elevation by a predetermined value. However, in some cases, themeans providing a third path can be omitted.

Thus, in the preferred embodiment of the invention, there are threevalves, a first one of which permits fluid to flow from the lowerportion of the cable to a higher portion of the cable, a second one ofwhich permits fluid to flow from the higher portion of the cable to thelower portion of the cable at a limited rate, e.g. 0.25 gallons perminute, and a third one of which permits fluid to flow temporarily toeither the atmosphere or the lower portion of the cable when the fluidpressure across the third valve exceeds a predetermined value, e.g. theweight of the fluid above the third valve plus 30 psi.

The invention also includes an electrical cable system in which thecable, either a pipe-type or self-contained cable, includes at least oneportion at an elevation higher than any other portion or portions at anelevation higher than any above atmospheric pressure supplied thereto bya source of fluid under pressure above atmospheric pressure, theportions being hydraulically separated by stop joints which preventfluid flow between the portions themselves, and an automatic valvesystem comprising valves which by-pass the stop joints and permit fluidto flow from lower elevation portions to the higher elevation portionsbut permit and limit the flow of fluid from the higher elevationportions to the lower elevation portions. The valve system may alsoinclude a relief valve which reduces the fluid pressure in the portionor portions at higher elevations when the fluid pressure across therelief valve exceeds a predetermined value.

The invention further includes a method of controlling fluid flow inelectrical cable systems which comprises allowing fluid flow through afirst path only in a first direction and allowing fluid flow through asecond path in a second direction only at a limited rate. The method mayfurther comprise allowing fluid flow through a third path in the seconddirection only if a predetermined pressure is exceeded and preventingfluid flow in the third path if the predetermined pressure is notexceeded. The first direction may be from a lower elevation to a higherelevation and the second direction may be from the higher elevation tothe lower elevation.

The invention further includes a method of controlling the flow of fluidfrom an electrical cable system in which the cable extends from a regionof lower elevation to a region of higher elevation. The cable systemcomprises at least one stop joint. The method comprises pumping thefluid from the lower elevation to the higher elevation through thecable; allowing the fluid to by-pass the stop joint as it is pumped fromthe lower elevation to the higher elevation; and allowing the fluid toflow from the higher elevation to the lower elevation, by-passing thestop joint, at a reduced rate when the fluid is not being pumped. Themethod can further comprise allowing the fluid to flow from the higherelevation to the lower elevation, by-passing the stop joint, at a higherrate, if a predetermined pressure is exceeded and preventing the flowfrom the higher elevation to the lower elevation at the higher rate whenthe predetermined pressure is not exceeded.

Other valves conventionally used with a stop joint can be included inaddition to the valves of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a pressurized cable system inaccordance with one embodiment of the present invention;

FIG. 2 is a cross-sectional view of an exemplary "pipe-type" cable whichcan be used in the system of FIG. 1;

FIG. 3 is a cross-sectional view of an exemplary "self contained" cablewhich can be used in the system of FIG. 1;

FIG. 4 is a schematic drawing of an automatic by-pass valving system ofthe present invention, which can be used in the cable system of FIG. 1;

FIG. 5 is a schematic drawing of another embodiment of the automaticby-pass valving system, which can also be used in the cable system ofFIG. 1; and

FIG. 6 is a schematic drawing of a pressurized cable system whichdiffers from the cable system shown in FIG. 1 and in which the valvesystem of the invention can be used.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 is a schematic drawing of a high voltage cable system 10 inaccordance with one embodiment of the present invention. The systemcomprises a power station 12, a pumping station 14, an electrical cable16 comprising a plurality of cable portions or sections 16a-16d, aplurality of stop joints 18a-18c, automatic by-pass valving systems20a-20c in accordance with the present invention and associated witheach joint 18a-18c, and lines 22a-22c to electrical power users. Thenumber of cable portions 16a-16d, joints 18a-18c and associatedautomatic by-pass valving systems 20a-20c can vary based on the lengthof the system, as is known in the art. The upper end of the cable, at16d, is at a higher elevation than the power station 12, and the pumpingstation 14 supplies a fluid, e.g., a dielectric insulating fluid under apressure above atmospheric pressure to the cable portions 16a-16d. FIG.1 also illustrates the location of a rupture or break 70 in the cableportion 16b. Conventionally, the pumping station 14 contains sensing andcontrol apparatus which, when there is a significant drop of thepressure of the fluid in the cable, e.g., because of a break of rupture,stops the supply of fluid to the cable.

The cable 16 comprising sections or portions 16a-16d can, for example,be a "pipe-type" cable of the type shown in FIG. 2 or a "self-contained"cable of the type shown in FIG. 3, but the invention is applicable tothe control of fluid outflow from other systems having pipes or ductsfilled with fluid under pressure, for example.

In a pipe type electrical cable, the electrical conductors areseparately insulated from each other and are contained in a metal pipeand a dielectric fluid, under pressure above atmospheric pressure, fillsthe spaces within the pipe not occupied by the conductors and theircoverings. FIG. 2 illustrates, in cross-section, one known type of pipecable but the invention is applicable to other types of pipe cables.Although the cable shown in FIG. 2 is identified by the referencenumeral 16a, the other sections 16b-16d can be of the same construction.

The cable shown in FIG. 2 comprises three identical units 23-25 and onlythe unit 23 will be described in detail. The unit 23 has a conductor 26composed of stranded wires of high electrical conductivity, e.g., copperor aluminum wires. The conductor 26 is encircles by an innersemi-conductive screen 27, insulation 28, an outer semi-conductivescreen 29, metal tapes 30 and skid wires 31 and 32.

The units 23-25 are loosely received in a fluid tight, metal pipe 33,such as a steel pipe, with a conventional corrosion protecting covering34. The spaces within the pipe 33 not occupied by the units 23-25 arefilled with a dielectric fluid 35 under pressure above atmosphericpressure. Such spaces provide fluid channels. The fluid can be static orcirculated in a known manner and can, for example, be a conventionalsynthetic or natural fluid.

A three conductor, self-contained cable of a known type is illustratedin FIG. 3. However, instead of being bound together, as describedhereinafter, the units 36-38 can be individual units not bound togethersince each unit 36-38 constitutes a cable which can be used withoutfurther coverings.

The units 36-38 are identical and only the unit 36 will be described indetail. The unit 36 comprises a central conductor 39 which can be madeof metal segments, such as segments of copper or aluminum, which definea central duct or fluid channel 40. The conductor 39 is encircled by aninner semi-conductive screen 41, insulation 42, an outer semi-conductivescreen 43, a lead or aluminum sheath 44, a blindage layer 45, e.g., alayer of metal tape, and a plastic sheath 46. Thus, the unit 36, andhence the units 37 and 38, are self-contained and can be used withoutfurther coverings.

However, if desired, the units 36-38 can be bound together within aknown type of armoring layer 47 which can be covered by a protectivelayer 48 of a known type, e.g., a bituminous material, and/or of thermalinsulating material. The spaces within the armoring layer, and the units36-38, conventionally are filled with a filler 49 which can be jute,rubber or a plastics material.

FIG. 4 is a schematic diagram of a stop joint 18b coupled to twopipe-type cables 16b, 16c and the automatic by-pass valving system 20bin accordance with one embodiment of the present invention. AlthoughFIG. 4 illustrates only the automatic by-pass valving system 20b, theother automatic by-pass valving systems 20a-20c can be the same. Thestop joint 18b permits the passage of the insulated conductors 26 butnot the surrounding insulating fluid 35. Of course, the stop joint 18bis illustrated only schematically and the various conventionalmechanical and electrical connections are not shown. The plug 50represents the portion of the stop joint 18b which prevents flow of thefluid 35 between the pipes 33 of the cable sections 16b and 16c. Anyconventional joint can be used.

Each of the automatic by-pass valving systems 20a-20c, in accordancewith the embodiment shown in FIG. 4, comprises first and second fluidconveying means such as fluid conduits or pipes 51 and 52, a check valve53, and a flow-limiting valve 54. Preferably, a relief valve 55 is alsoprovided. Each valve 53, 54 and 55 is between the first and secondconduits 51 and 52 of the by-pass valving system 20b. In thisembodiment, the valves are between the first and second conduits 51 and52 in parallel.

The portions of the automatic by-pass valving system, joint 18b and thecable 16b to the right of the dotted line A--A are referred to as the"lower elevation" portions of the electrical cable system, and theportions to the left of the dotted line will be referred to as the"higher elevation" portions of the system. It is to be understood thatthe terms "lower elevation" and "higher elevation" are relative termsdescribing portions of the system with respect to the highest end andlowest end of the cable system 10. Thus, as shown in FIG. 6, theelectrical cable system can have a portion 16c with an end connected tothe stop joint 18b which is lower than the cable portion 16b which isconnected to the stop joint 18b and which is lower than part of thecable portion 16a connected to the stop joint 18a. However, there arecable portions, such as part of the cable portion 16c and the cableportion 16d which are higher in elevation than the stop joint 18b andpart of the cable portion 16a so that the force of gravity appliespressure to the fluid in the direction from the cable portion 16d to thelower part of the cable portion 16a. Accordingly, as used herein, theexpression "higher elevation" is intended to include a valve system 20bconnected as shown in FIG. 6. Other stop joints 18c and 18a and valvingsystem 20c and 20a, above and below the illustrated portion of thesystem, have their own "higher" and "lower" elevation sides.

In normal operation, in the embodiments of FIGS. 1 and 6, the fluidflows from the lower elevation cable portion of each cable section16a-16d through the automatic by-pass valving system 20a, 20b or 20c tothe higher elevation cable portion of each cable 16a-16d, as describedhereinafter.

The first, lower elevation conduit 51 is coupled for fluid flow to thelower elevation cable portion 16b. The second, higher elevation conduit52 is coupled for fluid flow to the higher elevation cable portion 16c.

The check valve 53, which preferably is a positive-sealing check valve,has a lower elevation end 53a couples to the lower elevation conduit 51.The check valve 53 also has a higher elevation end 53b coupled to thehigher elevation conduit 52. The check valve 53 only allows fluid flowonly from the first lower conduit 52 to the second higher elevation pipe52.

The flow-limiting valve 54, which preferably is a variable differentialflow-limiting valve, has a lower elevation end 54a couples to the lowerelevation conduit 51. The flow-limiting valve also has a higherelevation end 54b coupled to the higher elevation conduit 52. Theprimary function of the flow-limiting valve 54 is to allow fluid flow,in a second direction, from the higher elevation cable portion 16c tothe lower elevation cable portion 16b, at a limited rate. The limitedrate is substantially less than the rate of unrestricted flow. Apreferred rate is less than about 0.25 gallons per minute (GPM), forexample, but can be in the range from 0.10 to 0.50 GPM depending uponthe fluid loss considered to be acceptable and which meets therequirements of the environmental regulations. Any valve allowing thepassage of a controlled columnetric flow over a wide range of pressuredifferential, can be used. In this application, operation over apressure differential of 500 psid-0 psid (pound per square inchdifferential) is preferred. Variable differential flow-limiting valvesare also referred to as floating orifice valves or uniflow valves in theart. A model 30-21-001 valve from Pirelli-Jerome, Inc., Beaufort CountyIndustrial Park, Beaufort, S.C., for example, can be used. Such Pirellivalve is a floating orifice valve which functions similarly to apressure regulating valve in series with an adjustable orifice valve.

The relief valve 55, which preferably is a positive sealing reliefvalve, has a lower elevation end 55a which is coupled to the lowerelevation conduit 51, and a higher elevation end 55b coupled to thehigher elevation conduit 52. The relief valve 55 allows flow in thesecond direction, from the higher elevation conduit 52 to the lowerelevation conduit 51, only when the fluid pressure on the higherelevation end 55b of the valve 55 exceeds the pressure on the lowerelevation end 55a by a predetermined value, such as, for example, theweight of the fluid above the valve 55 plus 30 psi. The purpose of therelief valve 55 is to avoid a large increase in the pressure applied tothe check valve 53 and the flow limiting valve 54 when a rupture orbreak occurs, such rupture or break causing the fluid pressure at lowerelevation to become very small whereas the fluid pressure at elevationsabove such valves will, for a short time, be very large. If the valves53 and 54 can withstand such fluid pressure differential, the reliefvalve 55 can be omitted. Also, while it is preferred that the lower end55a of the relief valve 55 be connected to the lower elevation cablesection, such as by way of the conduit 51, the lower end 55a of thevalve 55 can be vented to the atmosphere or ambient because, in thelatter case, the fluid loss would be relatively small. When the fluidpressure differential drops below the predetermined value, the reliefvalve 55 closes again. As stated, the predetermined pressure differencepreferably is the weight of the fluid above the stop joint 18b, plus anamount such as 30 psi, which will reduce the pressure on the valves 53and 54 to an to an acceptable value. However, depending upon thetolerance of the valves 53 and 54 to fluid pressure differential, therelief valve 55 can discharge fluid until the pressure differential isgreater or less, but preferably, discharges when the pressuredifferential is at least greater than the weight of the higher elevationfluid. The relief valve may be a piston type positive sealing reliefvalve, such as the Teledyne Farris Relief valve, available from TeledyneCorporation, for example.

Operation of the cable system 10 and automatic valving systems of thepresent invention will be described with reference to FIGS. 1 and 4.During normal operation, fluid is pumped by the pumping station 14 fromthe lower elevation to the higher elevation through the cable sections16a-16d. (See FIG. 1). The fluid flows upwardly around the stop joints18a-18c by way of the conduits 51 and 52 and the check valve 53. (SeeFIG. 4). Fluid may, if desired, also flow to the higher elevationthrough the flow-limiting valve 54. If the pressure at the elevationsabove any of the stop joints 18a-18c exceeds the pressure at a lowerelevation, such as if the pumping station stops pumping fluid orpressures rise within the cable due to thermal expansion, the fluidabove a stop joint 18a-18c can flow to the lower elevation at thelimited rate, through the flow-limiting valve 54. Generally, suchpressure changes are slow in nature and can be adequately relievedthrough the slow flow of the flow-limiting valve 54.

If there is a cable rupture or break, as indicated at 70 in FIG. 1 whichpermits the fluid to flow out of the pipe 33 or a duct 40 into theambient, the controls at the pressurization plant 14 will sense a suddenloss in fluid pressure and either restrict or stop the pumping of fluidinto the cable system. While the fluid between the stop joint 18b andthe break 70 can flow out of the cable under the influence of gravity,the flow-limiting valve 54 in the by-pass valving system 20b, will onlyallow a small additional flow of fluid from above the stop joint 18b tothe lower elevations and out the break 70. This small flow limits thedamage to the environment, while preventing contaminants, such as wateror dirt, from entering the cable 16b through the break 70.

Ruptures or breaks in the cable caused by heavy equipment, lightning, orother catastrophic events, can cause large pressure surges through thecable system 10. To protect the valves 53 and/or 54, the relief valve 55preferably is provided to allow for the release of fluid to relieve thepressure surge before it can damage the valves 53 and/or 54. When thethreshold pressure of the relief valve 55 is exceeded, the valve 55opens and fluid in the higher elevation cable portion 16c and 16d willbe released to the lower elevation cable portion 16b, through theconduit 51. Such fluid will escape through the break 70 as well. Whenthe pressure at elevations above the by-pass valving system 20b drops tothe threshold pressure, the relief valve 48 closes and only a smalladditional amount of fluid will flow to lower elevations through theflow-limiting valve 46, as discussed hereinbefore. The relief valve 55should be able to at least support the weight of the fluid at elevationsabove the by-pass valving system without opening. The threshold pressureis therefore preferably equal to the total weight of fluid in all thecables above the automatic valving system 20, here cable portions 16cand 16d, plus a tolerance, as discussed hereinbefore.

The automatic by-pass valving system of the present invention may beoptionally fitted with additional valves to assist in the initial fill,calibration, monitoring or shutdown of the by-pass valving system, as isknown in the art. For example, one or more manually operable isolationvalves may be provided at opposite sides of the relief valve 55, thecheck valve 53 and the flow-limiting valve 54. In the embodiment of theautomatic by-pass valving system 21 shown in FIG. 5, manually operableisolation valves 72 and 74 can be provided at respectively oppositesides of the relief valve 55. Manually operable isolation valves 76 and78 can be provided at opposite sides of the flow-limiting valve 54 andthe check valve 53. The isolation valves 72, 74, 76 and 78 are normallyopen during operation of the system. They can be closed to shut down thesystem. Any conventional isolation valve may be used.

Preferably, a manually operable valve instrument port 80 is preferablyprovided proximate the flow-limiting valve 54, to calibrate the valve.Preferably, manually operably valve instrument ports 82 and 84 areprovided to enable monitoring and calibration of the system. Appropriatevalve instrument ports are known in the art.

A conventional manually operable by-pass valve 86 is also provided toassist in the initial fill of the cable. The manually operable by-passvalve 86 may be connected between the first and second conduits 51 and52, in parallel with the check valve 53, flow-limiting valve 54 andrelief valve 55. The manually operable by-pass valve 86 is normallyclosed, is opened only during initial fill of the cable. The by-passvalve 86 is the valve normally used in the prior art to prevent fluidflow around a stop joint when the cable is ruptured. Manual valveservice ports 88 and 90 can also be provided proximate the manualby-pass valve 86. These valves are also closed during normal operationbut can be opened during the initial fill of the cable. Appropriatevalves are known in the art.

The automatic by-pass valving system 21 of FIG. 5 operates in a similarmanner to the valving system of FIG. 4. During normal operation, fluidflows from the pumping station 14, through the first cable 16b, into thefirst conduit 51 through the isolation valve 78, through the check valve53, through the isolation valve 76 and into the next cable 16c throughthe second conduit 52. In case of a cable break or rupture, fluid isallowed to flow towards the break or rupture through the isolation valve76, the flow-limiting valve 54, the isolation valve 78, and into thelower elevation cable through the conduit 51. As described hereinbefore,the downward flow is slow as the rate of the flow-limiting valve 54 is,preferably, not more than about 0.25 GPM. The degree of cable pressureis decided upon and controlled at the pumping station 14, as is known inthe art.

If there is a sudden pressure surge due to impact, explosion or thesudden release of downstream pressure causing a high pressuredifferential across the relief valve 55, the valve 55 opens. Fluid canthen flow through the isolation valve 72, the relief valve 55, theisolation valve 74 and out the by-pass valving system 21 through conduit51, until the high pressure differential is reduced to a predeterminedvalue. When the pressure differential returns to the threshold pressure,e.g., the weight of the fluid above the stop joint plus about 30 psi,the relief valve 55 closes and fluid flow to lower elevations is limitedto that allowed by the flow-limiting valve 54.

It will be apparent to those skilled in the art that the particularconfiguration of connections between the valves in FIGS. 4 and 5 aremerely illustrative and other configurations are possible and within thescope of the present invention. It is also apparent that othermodification may also be made without departing from the principles ofthe invention.

Although the specific example of the use of the automatic by-passvalving system with a pipe type cable has been described, it will beapparent to those skilled in the art that the automatic by-pass valvingsystem can be used with self-contained cables, the by-pass valve systembeing connected to the duct or ducts, or fluid channels, of theself-contained cables rather than to the pipe of the pipe type cable.

While the above embodiments specifically relate to an electrical cable,the automatic by-pass valving systems and methods of the presentinvention are useful in any piping or duct system which supplies fluidsunder pressure in one direction and which runs a risk of theunrestricted loss of fluid into the environment due to a rupture orbreak in the pipe or duct.

I claim:
 1. An electrical cable system in which the cable contains afluid under pressure above atmospheric pressure and the cable has afirst portion at a lower elevation and a second portion at a higherelevation, said system comprising:a source of fluid under a pressureconnected to said cable for supplying said fluid to the interior of saidcable; a stop joint between said first portion and said second portionof said cable, said stop joint blocking the passage of fluid betweensaid first portion and said second portion; an automatic by-pass valvingsystem coupled to the first portion and said second portion, saidby-pass valving system allowing fluid flow from said first, lowerelevation portion to said second, higher elevation portion around saidstop joint but limiting flow of said fluid from said second, higherelevation portion to said first, lower portion to a predetermined rate.2. The system of claim 1, wherein the by-pass valving system comprises:acheck valve coupled between said first, lower elevation portion and saidsecond, higher elevation portion, the check valve allowing said fluid toflow substantially only from said first lower elevation portion to saidsecond higher elevation portion; and a flow-limiting valve coupledbetween said first, lower elevation portion and said second, higherelevation portion, said flow-limiting valve allowing fluid to flow fromsaid second, higher elevation portion to said first lower elevationportion at said predetermined rate.
 3. The system of claim 2, whereinsaid by-pass valving system further comprises a relief valve coupledbetween said first, lower elevation portion and said second, higherelevation portion, said relief valve allowing fluid to flow from saidsecond, higher elevation portion to said first, lower elevation portionsubstantially only when the fluid pressure in said second, higherelevation portion exceeds the fluid pressure in said first, lowerelevation portion by a predetermined amount.
 4. The system of claim 2,wherein the fluid is dielectric insulating fluid.
 5. The system of claim2, wherein said fluid is a conductor cooling fluid.
 6. The system ofclaim 2, wherein said cable comprises a fluid impermeable pipe looselyencircling at least one insulated conductor and said fluid is in anyspaces between said conductor and said pipe.
 7. The system of claim 2,wherein said cable is a self-contained cable comprising a duct for theflow of said fluid, a conductor and insulation and a sheath encirclingsaid conductor and said fluid is in said duct.
 8. An electric cablesystem in which the cable contains a fluid under pressure aboveatmospheric pressure and the cable has a first portion at a lowerelevation and a second portion at a higher elevation, said systemcomprising:a check valve permitting fluid flow at a first rate in afirst direction but preventing fluid flow in an opposite, seconddirection; a flow limiting valve permitting fluid flow at said secondlower rate in said second direction; and fluid conveying means connectedto said check valve and said flow limiting valve and for connecting saidcheck valve and said flow limiting valve to said first portion and saidsecond portion, so that said check valve permits fluid flow from saidfirst portion to said second portion and said flow limiting valvepermits fluid flow from the second portion to said first portion.
 9. Anelectric cable system of claim 8, further comprising a relief valvewhich permits the flow of fluid from one side thereof to the other sidethereof when the fluid pressure at said one side thereon exceeds thefluid pressure at said other side thereof by a predetermined amount,said fluid conveying means being connected to said relief valve forconnecting said one side of said relief valve to said second portion ofsaid cable and said other side of said relief valve to said firstportion of said cable.
 10. The electric cable system of claim 8, whereinsaid lower rate is about 0.10-0.50 gallons per minute.
 11. The electriccable system of claim 9, wherein said predetermined amount is at leastabout the pressure of the fluid at said second portion of said cable.12. The electric cable system of claim 11, wherein said predeterminedamount is about the pressure of the fluid at said second portion of saidcable plus approximately 30 pounds per square inch.
 13. The electriccable system of claim 9, further comprising a first isolation valvecoupled between the relief valve and said first portion of said cableand a second isolation valve coupled between the relief valve and saidsecond portion of said cable.
 14. The electric cable system of claim 8,further comprising a first isolation valve coupled between said checkvalve and said first portion of said cable and a second isolation valvecoupled between said check valve and said second portion of said cable.15. The electric cable system of claim 8, further comprising a firstisolation valve coupled between said flow-limiting valve and said firstportion of said cable and a second isolation valve coupled between saidflow-limiting valve and said second portion of said cable.
 16. Theelectric cable system of claim 8, further comprising first and secondisolation valves for isolating said check valve and said flow-limitingvalve from said first portion and said second portion of said cable. 17.The electric cable system of claim 8, further comprising a manuallyoperable by-pass valve coupled between said first portion of said cableand said second portion of said cable for permitting substantiallyunrestricted fluid flow between said first portion and said secondportion of said cable and preventing fluid flow through said manuallyoperable by-pass valve.